Quake Guy vs DooM Guy : Tough one. Quake guy can jump, and he has a grenade launcher... though his shotgun is way weaker than Doomguy's.

Cacodemon vs. a weakened DooM Guy with a Shotgun and ten shells : Doom guy. You only need 6 shells to put down a Cacodemon.

5 Barons of Hell vs. the CyberDemon : Dunno... it would take 25 precise rockets to take down those Barons, and that would take a long time. On the other side, the Baron's green goo doesn't do that much damage anyway.

Well, it's time for me to ask:
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Who Would Win in a Fight????
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whatever you want.

Quake Guy vs DooM Guy?

About evenly matched. Whoever gets the most lucky shots in.

Cacodemon vs. a weakened DooM Guy with a Shotgun and ten shells?

Doom guy. One cacodemon is plenty easy to take down, you only need 6 shells, and the ball lightning is easy to dodge so health isn't an issue.

5 Barons of Hell vs. the CyberDemon?

Cyberdemon. Remember map08, "tricks and traps"? Cybie always takes down at least 5 barons when I turn them against cybie.

Spider MasterMind vs. 6 Cacos, and 7 Barons?

I don't know. I don't have a map to reference off of like with the above question. Maybe i'll make one.

KITTY vs. IDSPISPOPD?
IDKFA vs. RAMBO?

What a damn stupid question.

Heretic Guy vs. Quake Guy vs. DooM Guy?

Now this is an easy one. Corvus (Heretic Guy) for sure. Weaponwise, he's pretty evenly matched, but he has tomes of power, morph ovums, wings of wrath, and invisibility artifacts and health potions he can carry around and use whenever he needs.